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Vibrios and Shellfish Safety

What is Vibrio parahaemolyticus?

Vibrio parahaemolyticus (Vp) is one of the many varieties of naturally occurring bacteria found in New York's marine waters. It is usually found in coastal waters, including areas where oysters, hard clams, and other shellfish can be found. Like many bacteria, Vp thrives under warm water conditions. During the summer, when the salinity is right and the seawater temperature rises, Vp concentrations can skyrocket.

How does it affect humans?

Clams, oysters and other bivalve shellfish are filter feeders; they strain plankton and other marine organisms from the waters. During the summer months, when conditions are most favorable to Vp growth, shellfish are more likely to filter and ingest significant amounts of Vp from surrounding waters. Under warm conditions, the concentrations of Vp in shellfish can climb to very elevated levels.

If shellfish are not kept cool after they have been harvested, the Vp concentration may continue to rise to levels harmful to humans. Eating raw or undercooked clams and oysters that contain a elevated concentrations of Vp may induce gastrointestinal illness in humans. The symptoms of a typical, food borne, Vp infection include abdominal cramping, nausea, vomiting, fever, chills and diarrhea. Typically the illness lasts about three days and requires no treatment beyond replacing lost fluids. Occasionally the infection can be more severe in people with compromised immune systems, such as children and the elderly. While the most common type of Vp infection is caused by ingestion, it is also possible to get a Vp skin infection if an open wound is exposed to warm sea water with significant levels of Vp.

How can you avoid a food borne Vp infection?

You can avoid contracting a Vp infection by not eating raw or undercooked shellfish.

How is DEC working to prevent Vp outbreaks?

DEC has implemented a Vp Control Plan to give commercial shellfish diggers specific instructions on how to handle harvested shellfish to inhibit the growth of Vp. Highlights of the plan include requiring diggers to keep clams and oysters in the shade during the warmer weather months and to quickly get their product to a cooler environment, either by icing or mechanical refrigeration. Shellfish shippers are also required to keep shellfish within a certain temperature range to reduce bacterial growth.

How can recreational diggers reduce their risk for Vp infection?

Using common sense when handling clams and oysters, recreational diggers can go a long way in reducing their risk. While you are harvesting, keep your shellfish in the shade and avoid keeping any shellfish in direct sunlight. Once you have finished digging the shellfish, place them in a cooler, or on ice, or in some type of refrigeration as quickly as possible. Be careful not to leave the shellfish in standing water. Storing shellfish inside a hot vehicle, with no means of cooling, can cause Vp levels in the shellfish to double in less than 15 minutes.